查看更多>>摘要：Low thermal conductivity limits the application of phase change material (PCM) in a battery cooling system as a passive thermal management system. Leaf veins are extensively represented as a classical branching structure that absorbs heat in the energy transfer systems of plants. To improve the overall thermal conductivity, this paper proposes a PCM battery thermal management system coupled with a leaf vein fin. First, by comparing different topology parameters, a topological optimization structure using COMSOL simulation is adopted to design a bionic leaf vein fin for heat transfer. Subsequently, we perform a numerical ANSYS simulation for a PCM cooling system coupled with a leaf vein fin based on the heat generation features of a LiFePO4 battery. Consequently, the leaf vein fin coupled with PCM can efficiently remove heat from the cell surface and uniform the cell surface temperature. By comparing battery temperature and PCM melting, the leaf vein fin cooling systems demonstrates a 34.6% increase in temperature drop compared to that of the traditional rectangular fin. Eventually, the economical cooling parameters for uniformly stabilizing the cell temperature in the appropriate operating range are derived as phi = 0.4, t(w) = 26 degrees C, and d = 4 mm by comparing different volume fractions, wall temperatures, and fin thicknesses.
查看更多>>摘要：The present study aims at investigating the energy, exergy, and economic performance of an innovative multisource renewable hybrid energy system for small-scale combined heat and power (CHP) applications. The system is based on a transcritical organic Rankine cycle (ORC) able to exploit solar and biomass sources, through a concentrated solar power unit and a biomass boiler. A thermo-economic model has been developed and a parametric analysis has been implemented to define the proper configuration of the hybrid system balancing energy and economic purposes. The investigation, performed for a residential complex in Southern Italy, highlights that the suitable hybridisation of biomass and solar energy increases the useful production and system flexibility compared to the single-source configurations. The proposed small-scale system guarantees a 48.9% decrease in the biomass consumption compared to the corresponding biomass-only apparatus, increases the exploitation (+8.8% of electric production) of low solar radiations that are not adequate to feed a full-solar ORC, also overcoming the stochastic and intermittent characteristics of the solar source. The comparison with the conventional scenario, where the electric grid and natural gas boilers satisfy the energy demands, separately, demonstrates that the suggested solar/biomass hybrid ORC system guarantees a 24.2% primary energy saving, a 53.5% decrease in the unit electric and thermal production costs, and a 57.7% drop in greenhouse gas emissions, with a payback period equal to 7.5 years.
查看更多>>摘要：Cement plants are one of the most energy consuming industries in which a large amount of heat energy is lost into the atmosphere causing the increase of environmental issues and leading to the rise of cement production energy cost. Recently, waste heat recovery systems such as steam and Rankine cycles have received much attention by researchers and industrial sectors for power production application to enhance the system efficiency. However, the existing waste heat recovery systems present different drawbacks. This paper proposes, for the first time, a new technique of recovering cement plants waste heat based on Stirling engine technology. The modelling of a Gamma type Stirling engine was conducted for recovering the waste heat released from the clinker cooling process. Furthermore, the non-ideal adiabatic model was used for engine designing in MATLAB software. For model validation step, the results obtained from the present study have been compared with experimental data of Lewis Research Center in the National Aeronautics and Space Administration and previous numerical models. The comparison findings have shown a high accuracy of the current model. The effect of several geometrical and physical specifications on Stirling engine performances was studied to obtain the best engine design. The results showed that maximum efficiency can be achieved by increasing the regenerator porosity up to 79 % and by decreasing the regenerator length to 0.015 m. A matrix wire diameter of 50 mu m has been found as an optimum value regarding the high output power generated and acceptable heat input required. The parametric analysis of heat exchangers geometries has revealed that the increase of the heater and cooler tube lengths reduces the engine performances. However, the rise of heater and cooler tube inner diameters could enhance the power and efficiency. Furthermore, it was found that the variation of phase angle has an important influence on Stirling engine outputs, thus the consideration of 90 degree as phase angle is more suitable for engine design which will be able to produce 1641.36 W with a thermal efficiency of 21.29 %. Additionally, it was concluded that the augmentation of pressure and rotational speed increases the engine power. Finally, it was shown that the rise of working gas mass enhances the engine output power but increases the heat input requirement. This work demonstrates the potential of using Stirling engine technology for cement plants waste heat recovery applications and highlights its ability to produce high output performances.
查看更多>>摘要：A summary of the research undertaken on poly-aluminum sulfate is performed revealing several disagreements on important thermal properties of the material. Nevertheless, the energy density reported highlights that the material is promising for thermochemical heat storage (THS). A thorough thermal analysis (TA) of (Al-2(SO4)(3).xH(2)O) is conducted using TA devices and the ICTAC kinetics committee recommendations, to identify its thermal properties, its most stable form (Al-2(SO4)(3).18H(2)O, and the conditions of its use for low-temperature THS (80 C and 125 C under atmospheric pressure. The material decomposes in four endothermic stages as shown in the thermal curves and illustrated by possible reaction formulas, three of which are dehydrations followed by a final decomposition. The non-isothermal kinetics of the dehydration for PAS has been determined by the methods of Coats-Redfern (CR) and Achar-Brindley-Sharp (ABS) with 19 different reaction models. It is found that most reaction models exhibit a linear trend. The Janders reaction model is appropriate for the first dehydration with an activation energy of ca. 33.248 kJ/mol by CR and 30.759 kJ/mol by ABS, respectively. Both the power law and the Avrami-Erofeev model can be used for the second stage with an activation energy of ca. 235 kJ/mol. The overall kinetics modeling for aluminum sulfate hydrate is successful for PAS implying the substitution of aluminum sulfate with PAS in applications.
查看更多>>摘要：High temperature thermal insulation performance plays a crucial role in the application of thermal contact resistance precision measurement to reduce systematic heat loss and ensure 1D axial heat flow. In this paper, a compound insulation system composed of carbon fibrous materials and multilayer insulation (CFMLI) with non-interlayer-contact space was proposed in terms of high temperature sustainability, low thermal conductivity and thermal performance stability. An experimental set-up was designed and fabricated to measure the temperature distribution and the effective thermal conductivity of CFMLI as a function of temperature (800 K-1325 K). The experimental results showed that the temperature gradually decreases from inner to external radius of CFMLI, and a temperature jump of 40 K-80 K appears at the interface between two segments under vacuum conditions. It also reveals that the thermal performance of CFMLI is strongly dependent on the gas pressure and the number of reflective layers, while it is hardly affected by the filling materials when the temperature is above 1050 K. Meanwhile, the effective thermal conductivity of CFMLI varies around 0.2 W/m/K for two levels of pressure (10(-4) Pa and 0.1 MPa), and it decreases by 14.7% when the number of reflective layers increases from 6 to 21 at 1325 K. Additionally, a theoretical model with thermal resistance network was developed for heat transfer analysis of CFMLI. The model could predict the external temperature of CFMLI with high accuracy so that the difference between the theoretical results and experimental data was less than 2.61%.
查看更多>>摘要：Composite phase change material (CPCM) cooling is an essential method to ensure better performance of battery thermal management system (BTMS) due to high latent heat. However, long recovery time of CPCM makes it unaffordable especially during continuous high rate discharge-charge cycles. In order to reduce the energy consumption while enhancing the latent heat recovery efficiency, a novel hybrid BTMS architecture coupling with CPCM and liquid cooling is proposed. Liquid cooling is employed to recover the latent heat of PCM. To enhance the heat transfer in BTMS, the structural layout of liquid cooling arrangement is investigated. Meanwhile, mass fraction of expanded graphite (EG) and bulk density of CPCM are considered. Specially, the experiments are conducted to verify the effectiveness of present hybrid BTMS. In solidification, temperature performance especially temperature uniformity is not ideal. Therefore, a novel successive multiple attribute decision making (MADM) algorithm is employed to achieve optimized temperature difference, maximum temperature, solidification rate and mass of CPCM. In MADM algorithm, the order preference by similarity to ideal solution (TOPSIS) is coupled with the analytic hierarchy process (AHP) to solve the multi-objective discrete optimization problem. Results indicate that the optimal solution can make the maximum temperature and temperature difference at the lowest level of 317.51 K and 3.45 K at discharge rate of 4C. Meanwhile, the latent heat of CPCM is improved by about 27.5% at charge rate of 2C. The solution can improve the long-term reliability for the BTMS and the safety and service life for battery module.
Palacz, MichalHaida, MichalSmolka, JacekNowak, Andrzej J....
13页
查看更多>>摘要：The dynamic development of R744 refrigeration cycles has been observed throughout recent years. State-of-the-art R744 is equipped with ejectors or ejector modules to increase the overall system coefficient of performance (COP). That performance improvement can be achieved only with the proper ejector design and corresponding control strategies. Therefore, numerous computational studies on the ejector performance and fluid flow inside the device have been conducted by various groups of researchers. Unfortunately, experimental studies on twophase R744 are fairly limited, especially in terms of fluid flow visualisation. For that reason, this study is focused on two-phase flow and mixing visualisation inside the R744 ejector designed for an industrial-scale refrigeration system. Experiments were conducted in the experimental R744 vapour compression rack with the dedicated ejector tests section. The mixing section of the ejector used in this study was made of transparent material to enable flow visualisation experiments. A high-speed camera and additional light sources were used to capture the flow inside the mixing section. The experiments were conducted for the ejector working with unsteady operation in two modes: the suction nozzle closed and standard operation with both ports open. Then, the experimental results were used to evaluate the expansion angle for the subcritical, critical, and supercritical MN inlet conditions. The collected results showed that the expansion angle increased with increasing mass flow rate in the motive nozzle. In particular, the expansion angle for the subcritical case was equal to approximately 2.75 degrees, while for the supercritical case, it was equal to 5.95 degrees. The mixing angle for most of the investigated cases was equal to approximately 25 degrees. The increase in the pressure lift increased the mixing angle up to 40 degrees. The unsteady operation of the ejector mixing section showed a pressure lift equal to approximately 10.0 bar, which resulted in a decrease in the SN mass flow rate but did not affect the vapour compression test rig performance.
查看更多>>摘要：This paper proposes an analysis for cattle manure-fed anaerobic digestion reactor (ADR), with biogas upgrading technologies, to be integrated into a CCHP system. The aim is to substantiate whether such a system will present economic, environmental, and energy-related benefits over conventional CCHP systems. Eight CCHP configu-rations have been modeled and optimized. The proposed CCHP systems are applied to an office building, for quantifying and analyzing the system performance for satisfying energy loads within the European building sector in a heating-dominated climate. The CCHP system with an integrated ADR, with a biogas boiler, deploying the electric load operational strategy yields the best results. This system presents an overall performance score of 151.1%, after achieving the best carbon emissions reduction ratio of 93.7%, and the best primary energy saving ratio of 32.0%.
Aneli, StefanoGagliano, AntonioDemir, HasanTina, Giuseppe Marco...
13页
查看更多>>摘要：In the last year, a continuous deeply increase in energy demands for cooling purposes is observed. Such energy needs are mainly satisfied through conventional vapour compressor chiller (VCC), which foresee the use of electricity usually generated through conventional energy sources. As an alternative, solar cooling plants offer a reliable and environmentally friendly for producing, in a sustainable way, cooling energy. This paper presents the analysis of the performances of an adsorption chiller (ADS) driven by solar energy operating in the Mediterranean area. In particular, this research aims to highlight the effectiveness and constraints of using photovoltaic/thermal (PVT) panels as the energy source of a heat-driven adsorption chiller (PVT ADS). Since the PVT allow producing both thermal and electrical energy it is of fundamental importance to investigate the effects of the operative temperatures on the efficiency of the whole PVT-ADS system. The analysis was conducted developing a dynamic simulation model for a solar cooling plant, for which the adsorption chiller's performances are derived by the 9.75 kW ADS, developed at the Gebze Technical University, Turkey. Cooling and power production has been explored as a function of the regeneration temperature of the ADS chiller. This analysis allowed us to point out the best design for the investigated PVT-ADS system. As a result, a regeneration temperature of 70 ? for a volume of the solar tank of 60 l/m(2) of PVT panel was defined. The investigated PVT-ADS, composed of 49.0 m(2) of glazed PVT panels achieves 51.9 and 40.3 kWh of cooling energy and electrical production respectively, during a typical summer day. Moreover, the comparison between the proposed PVT-ADS with a vapour compressor chiller driven by conventional PV modules (PV-VCC) is proposed. Such comparison shows that the PV-VCC produce about 2.9 kWh of cooling energy, per kW of nominal cooling power installed, more than the PVT-ADS system. Instead, the PVT-ADS guarantees the highest net electrical yield. The results of this study demonstrate the effectiveness of using PVT system as a potential source for solar cooling plants in the Mediterranean area.
查看更多>>摘要：Porous medium had the advantages of high porosity, large specific surface area and three dimensional micro nano cross scale transfixion, which had been widely used in the fields of solar energy conversion, aviation, spaceflight, warship, automobile, combustion, catalysis, waste heat recovery and so on. Porous medium can be oriental designed to achieve excellent physical properties and heat transfer enhancement performances. When porous medium was used in the solar conversion systems and high-temperature applications, radiative transfer played a dominant role during the photon transfer and energy conversion process. The current state-of the-art review on the mechanism of radiative transfer in porous medium from macro scale to pore scale, the principle of radiative property measurement at environment temperature as well as high temperature was presented, with emphasis on the latest developments during the last decade. Advantages and disadvantages of solving the radiative transfer in the pore skeleton of porous medium based on both the geometrical optic theory and electromagnetic radiation theory were discussed in detail, in which the effects of polarization, diffraction and independent scatters in the pore skeletons of porous medium were considered or not. The literature review indicated that, in the further research on the radiative transfer in porous medium, the criteria for judging the limits of independent scattering of porous medium needed to be resolved and accurate radiative property measurement system at high temperature coupled with high precision inversion method needed to be developed.
NSTL
Elsevier